Investigation of temperature rise and spontaneous combustion behavior of lignite during spring transport from northern to southern regions

Spontaneous combustion of coal is a common occurrence during north-to-south railway transport in spring, leading to significant losses. Typically, it happens within days of mining, thereby necessitating a more in-depth investigation into the rapid ignition process. This study investigates the impact of the lignite freeze-thaw process on spontaneous combustion during winter transport in northern alpine regions. Low-temperature oxidation experiments compared raw and frozen coal under various conditions. Microscopic Bruner-Emmett-Teller (BET) and electron paramagnetic resonance (EPR) analyses were conducted to investigate pore structure and free radical concentration, while numerical simulations and field data assessed external factors. Results show that freezing increased YM lignite's low-temperature oxidation temperature by 28.36 °C and CO gas levels by 1752.58 ppm. Ice crystal formation due to internal water freezing expanded and cracked the coal structure, increasing porosity and exposing active sites. These changes enhanced self-heating, with oxidation accelerating upon rapid ambient temperature increases during southern transport. Wind speed also influenced micro-vortex and oxygen storage zones at the front and rear of carriages. This study identifies internal and external causes of spontaneous combustion and emphasizes the need for effective inerting strategies after freeze-thaw cycles.